The present invention relates to a brightness-regulating voltage-transforming circuit for high-pressure discharge lamp that provides better performance as compared with conventional circuits designed for the same purpose.
FIG. 1 is a circuit diagram of a conventional brightness-regulating voltage-transforming circuit for high-pressure discharge lamp previously designed by the same applicant of the present invention. As shown, the circuit mainly includes a voltage-transforming circuit consisting of a primary coil of a transformer T1, a first transistor Q2, a second transistor Q3, a first feedback resistance R10, a second feedback resistance R11, and a buffer inductance L1; and a brightness control circuit consisting of a transistor Q1, a buffer inductance L1, a diode D1, and other relevant resistors. The buffer inductance L1 for the brightness control circuit is the same one buffer inductance L1 included in the voltage-transforming circuit. That is, the brightness control circuit and the voltage-transforming circuit use the same one buffer inductance L1. When the transistor Q1 is made, current passes through the buffer inductance L1, and a part of energy accumulates on the buffer inductance L1. When the transistor Q1 is cut out, energy accumulated on the buffer inductance L1 is released to produce high temperature and noise interference that has adverse influences on the high-pressure discharge lamp.
It is therefore desirable to develop an improved brightness-regulating voltage-transforming circuit for high-pressure discharge lamp to eliminate drawbacks existing in the conventional circuit designed for the same purpose.
A primary object of the present invention is to provide a brightness-regulating voltage-transforming circuit for high-pressure discharge lamp that is able to reduce noise interference with the high-pressure discharge lamp and to increase the working efficiency thereof.
To achieve the above and other objects, the brightness-regulating voltage-transforming circuit for high-pressure discharge lamp of the present invention incorporates a diode into a brightness control circuit thereof. The diode is connected at an end to a juncture of a primary side of a transformer and an end of a buffer inductance, and at another end to a voltage source. When a transistor in the brightness control circuit is cut out, energy stored in the buffer inductance is regenerated and sent to the voltage source via the diode. As a result, the high-pressure discharge lamp has reduced noise interference and increased working efficiency.